Generally, four types of hydrokinetic devices have been tested in recent years. These are: horizontal axis turbines, vertical axis turbines, oscillating hydrofoils and a Venturi system where water is accelerated through a “choke system” to create a pressure drop that can be used to drive turbines. One example of a vertical helical turbine generator is known from U.S. Pat. No. 6,036,443 to Gorlov. Gorlov discloses a vertically oriented helical turbine which includes helical airfoil-shaped blades that are arranged in a spiral about a central shaft. The helical arrangement allows the turbine generator to be used in multidirectional fluid flows. An array of the turbines can be provided to increase power output. U.S. Pat. No. 4,384,212 to Lapeyre discloses a horizontally mounted helical turbine that is used on the surface to translate surface wave energy into electrical energy. Another surface mounted helical generator is disclosed in U.S. Pat. No. 2,154,397 to Cook.
Significant issues can be caused by known devices to marine life, which can be harmed by the rotating turbine blades. Various proposals to reduce the damage to marine life include encasing the turbine blades in a wire mesh cage, which adds to the expense of the installation and only act to protect larger animals such as turtles from coming into contact with the blades. However, the cages do nothing to prevent smaller fish from being harmed. Additionally, many proposed turbine blades can suffer damage from water-borne debris, and even shipping. Due to these problems, acceptance of hydrokinetic devices by local communities and environmentally aware groups has not been as strong as hoped for, and the reliability of the devices has been limited.
Most previous hydrokinetic generation proposals additionally involve providing a rigid housing or anchoring system to retain the generator. This can be prohibitively expensive, as it can involve anchoring installations, and also the installation of energy supply cabling and pipes. Additionally, once installed, there is typically not much flexibility to allow the turbines to move with different water flows. Various proposals exist to ameliorate these difficulties, including U.S. Pat. No. 4,849,647 to McKenzie discloses a floating helical turbine which is connected to a tether line by a flexible ball joint. U.S. Pat. No. 4,708,592 to Krolick et al. discloses a non-rigid helicoidal wind turbine that uses a flexible fabric sheet to form the helix, and which can be tethered to existing mast structures using swivel joints.
For the foregoing reasons, none of the suggested hydrokinetic energy devices have been successful in practice. Thus, there remains a need for an hydrokinetic energy generator that is efficient, can work in a variety of water flow situations possibly including an ice/water mix, and which does not harm marine life.
The present inventor has suggested exemplary arrangements of a hydrokinetic turbine that can be used in a hydrokinetic energy converter, and specifically to a helical auger turbine with an associated hydrokinetic generator. These auger turbines are described in U.S. Pat. Nos. 7,728,454; 7,938,622; 8,152,464; and 8,282,352, the entire contents of which are incorporated herein by reference. While the described turbines have been successful in practice, the launching of the turbines and the securing of the turbines into place in tidal water proved difficult, particularly when the turbine is made of a lightweight material or when there is insufficient ability to anchor or support both ends of the turbines.